The invention relates to a device for removing liquid media, in particular slag samples, from molten metal baths in iron or steel-making plants.
For removing samples of pig iron slag, for example, from a channel, flue or ladle, or for removing samples of steel slag from a converter, ladle, electrolytic refining furnace or treatment plant, there are various known methods for obtaining samples which are used for spectrometric analysis, but which have to be processed into a coin-shaped slag sample by means of a complex process.
Thus, according to one known method of slag sample removal, first of all a steel rod or similar metal implement is dipped into the molten metal. Simple steel tubes, steel rods or else more complicatedly shaped elements of greater surface area, which may be fastened on the outside of a dip sampling or dip temperature probe, may be used for this. When the metal implement is drawn out of the molten metal, the slag remains adhering to the metal surface. To prepare the slag sample for analysis, the slag must be knocked off the metal implement and the individual pieces of slag have to be processed further to form coin-shaped samples.
The processing of the slag may in some cases take up to one hour and makes this method of sample removal time-and cost-intensive. In addition to the high processing effort, false readings in the results of the analysis may also occur as a result of impure samples if the removal probes are used repeatedly and are consequently contaminated. In general, although the residual slag of the previous sample removal is thoroughly removed from the surface of the removal probe, in practice, false measured value readings caused by slag residues can scarcely be avoided.
Further false measured values are attributable to additives such as binders which have to be introduced into the slag sample during its preparation for analysis.
Such sample removal processes are described in U.S. Pat. No. 5,435,196.
This widely used procedure, consequently, still does not produce satisfactory results. In a novel method, the slag sample is sucked off of the surface of the molten metal with the aid of a suction probe. The probe essentially corresponds in its structural design to the probes used for sample removal from steel molten metal.
However, unlike the case of steel sample removal, the probe cannot be dipped into the molten metal, but instead has to be positioned with its inlet opening precisely in the layer of slag. This presents considerable difficulties in the case of thin layers of slag, since contamination of the sample with liquid metal can be avoided only with great difficulty. Sample removal with the aid of a suction probe is also scarcely possible in the case of certain metallurgical vessels, such as converters or treatment plants for example, on account of positioning difficulties. If the probe is dipped in too deeply, so that molten metal also gets into the sample mold, the slag sample is unusable for analysis.
The slag samples obtained are brittle and tend to crack, which may lead to fracturing of the samples. The samples can then no longer be used for spectrometric analysis.
Sample probes known in the art of steel sample removal, for example, with a cooling plate for the sample, also cannot be used for the removal of slag samples. Although such probes provide a sample of the molten steel that can be successfully analyzed, in that the steel forms a usable analysis surface on the cooling plate, such a probe usually does not produce slag samples which can be used for slag analysis, since the cooled slag on the cooling plate fractures or cracks and then can no longer be used for analysis.
Problems related to the dipping depth also do not exist in the case of steel sample removal, since the steel sample probe can be dipped into the molten metal to any desired depth to remove a steel sample, without risk, as in the case of slag sample removal, of contamination of the sample on account of incorrect positioning of the removal probe. Even with careful positioning of a steel sample probe in the slag layer, a pure slag sample can seldom be obtained.
The invention is therefore based on solving the problem of providing a removal device which allows simple and reliable slag sample removal from molten metals.
The problem is solved by providing a device for removing liquid media, in particular slag samples, which has an inlet opening located below the sample chamber, the cross section of the inlet opening being small, at least in one region, in relation to the cross section of the sample chamber, while the preferably cylindrically shaped sample chamber has a small height in relation to its cross section.
When the sample removal device is dipped into the layer of slag, the sample chamber is filled with slag through the inlet opening (mold inlet) located below the sample chamber. As this happens, an analysis surface forms against the cooling plate which forms the upper interior surface of the sample chamber. Contamination by the molten metal is prevented because the slag always enters the sample chamber first, on account of its lower specific gravity or density in comparison with that of the molten metal. The sample chamber is preferably shaped with respect to its volume in such a way that it is in any event completely filled only with slag, irrespective of the dipping depth of the sample probe.
The mold inlet, shaped narrower in comparison with the sample chamber, results in there being a highly distinct separating plane between slag and steel, even if a slag sample is taken from a layer of slag that is very thin and steel thus also gets into the inlet. The diameter of the inlet is dimensioned such that the slag located in the sample chamber freezes and cannot run back out of the sample mold when the probe is being taken out of the molten metal.
The inlet region ahead of the mold inlet may be designed in the form of a funnel, it being possible for the dimensioning of the funnel to be chosen such that reliable removal of the steel-free slag sample is possible even in the case of very thin layers of slag. Under such conditions, a wide funnel diameter with a small funnel height is chosen, so that access is possible to a relatively large surface area of slag, which then finds its way via the inlet funnel into the sample chamber of relatively small diameter, so that the sample chamber is completely filled by slag in spite of the thin layer of slag. In this case, the volume of the inlet funnel is preferably greater than the volume of the sample mold.
Furthermore, the problem which the invention addresses is solved by the sample chamber being bounded by a metal plate, which may have a wall thickness of less than 2 mm. This small wall thickness of the metal plate avoids excessively quick cooling of the slag surface, as a result of lower thermal conduction, whereby cracking of the slag sample is prevented.
With the sample surface formed on the metal plate, direct analysis of the slag sample is possible without processing, or with only little processing. To facilitate sample analysis further, in the slag chamber a sample ring may be provided, which encloses and stabilizes the sample during transport and analysis and which is removed from the sample chamber together with the slag sample. This prevents the sample from being fractured by mechanical stresses, in particular when it is removed from the sample chamber. In addition, the sample ring permits exact fixing of the sample in the adapter of an automatic analyzer.
For sample removal, the probe according to the invention is dipped in through the slag, whereupon the sample mold is filled on account of the ferrostatic pressure. If this pressure is inadequate, the probe can be dipped in further. The filling of the sample mold may be assisted by generating a negative pressure. The smallest possible inside diameter of the mold inlet prevents the sample from running out once the sample chamber has been filled and the probe is being removed from the slag.
The sample ring may be formed of a multi-part construction, in order to facilitate separation of the sample ring and sample-if this is necessary. However, the sample preferably remains in the sample ring, as described above. In addition, the sample ring may have notches or grooves in order to increase the adherence of the sample in the ring and, as a result, prevent the sample from falling out.
In another embodiment of the invention, the mold and metal plate are arranged below the elevation of the slag inlet, which is preferably designed in the form of one or more lateral inlet openings. The slag running in from above then solidifies on the thin metal plate and thus forms a usable analysis surface. In this embodiment, too, a sample ring may be provided for the removal and protection of the slag sample, but this ring is, in this embodiment, arranged above the metal plate. This embodiment consequently also allows direct sample analysis without further processing or preparation of the slag sample for the adapter of the analyzer. In this embodiment, the analysis surface lying at the bottom proves to be a particular advantage, since gas bubbles located in the liquid slag rise upwards, so that the analysis surface has fewer gas bubbles and consequently provides an analysis surface of better quality.
This embodiment is likewise advantageous in slag sampling from a low bath depth, such as for example in the slag channel on a blast furnace.
The invention is explained in more detail below on the basis of an exemplary embodiment represented in the drawing.